Bioluminescence is the production of light—with very little heat—by some organisms. The light-emitting substance (luciferin) in most species is an organic molecule that emits light when it is oxidized by molecular oxygen in the presence of an enzyme (luciferase). Bioluminescence is primarily a marine phenomenon occurring in many regions of oceans or seas. One example is the “milky sea” found in the Indian Ocean: In an area once measured to be about the size of Connecticut, the sea appears to glow an eerie blue at night— but it is actually bioluminescent marine bacteria called Vibrio harveyi.